Gas purification process



March 22, l949- J. MITCHELL ET A1.

GAS PURIFICATON PROCESS Filed Feb. 2o, 1945 2 sheets-sheet i .Nimml March 22, 1949. J. MITCHELL ET AL GAS PURIFICATION PRQCESS 2 Sheets-Sheet 2 Filed Feb. 20. 1945 IQOH ltr

HTTORNEY.

Patented Mar. 22, 1949 GAS PURIFICATION PROCESS John Mitchell and Herbert A. Gollmar, Pittsburgh, Pa., assignors to Koppers Company, Inc., Pittsburgh, Pa., a corporation of Delaware Application February 20, 1945, Serial No. 578,862

Claims.

The present invention relates to the liquid purification of byproduct coke-oven gas in respect of the separation and recovery of hydrogen sulphide and other absorbable gases therefrom. More particularly the invention relates to a process for the separation and recovery of hydrogen sulphide by scrubbing coke-oven gas with aqueous absorbent and actifying the absorbent for further scrubbing by heating it under subatmospheric pressure. The invention furthermore comprehends certain novel provisions in the method of quenching byproduct coke which constitute im provements both in the quenching method alone and in the economy of its operation in conjunction with the liquid purification process. Reference is hereby made to joint inventor Gollmars U. S. Patent 2,379,076 which relates to a similar process of gas purification.

A primary object of the present invention is to provide improvements in a process for separation and recovery of absorbable constituents from coke-oven gas whereby economy of operation is obtained.

Another object of the invention is to provide a process for purification of a fluid product of a coke oven, which process is more closely articulated with the system of a byproduct coke plant in order that overall advantages of economical operation can be obtained.

A further object of the invention is the provision of gas purification process and a cokequenching operation that are so adapted as to provide mutual interchange economies and especially utilization of Waste heat of such low thermal head that it has not previously been made available in the coke-plant system.

The invention has for further objects such other improvements and such other operative advantages or results as may be found to obtain in the processes or apparatus hereinafter described or claimed.

Brey stated, the present invention consists in a process for recovering an absorbable constituent such as hydrogen sulphide from coke- -oven gas, or other fluid product of a coke-oven A usual methods of quenching which include necessarily, for purpose of economy, recirculation of the quenching fluid, the above mentioned heating of the actified solution results in the simultaneous i cooling of the recirculated uid, and consequent economies in quencher operation are thereby realized.

It is the most common practice to quench hot coke immediately after its discharge from the coke oven with one spray or several intermittent circulated to quench a succeeding batch of hot coke.

The open-Water quenching system is in use in most coke plants particularly because it is simpler in operation and cheaper than more elaborate systems to install; and it is to this system that the present invention is particularly adapted whereby it is especially capable of widespread application and of providing greater heat economies.

In the accompanying drawings forming a part of this specification and showing for purposes of exemplication preferred apparatus in which the invention may be embodied and practiced but without limiting the claimed invention specifical- 1y to such instances:

Fig. 1 is a diagrammatic elevational view of apparatus for the continuous separation and recovery of hydrogen sulphide from coke-oven gas with indirect utilization of heat from the cokequenching system in the hydrogen-sulphide recovery; and

vFig. 2 is a diagrammatic elevational view of apparatus for the continuous separation and recovery of hydrogen sulphide from coke-oven gas with direct utilization of the heat and the vapors of quenching liquor in the hydrogen-sulphide recovery system.

Referring now to Fig. 1, coke-oven gas containing hydrogen sulphide flows through a pipe 2 into an absorber 4 containing packing and in which the said gas rises in counter-current contact with continuously descending absorbent, for example, an aqueous solution of sodium carbonate and acid carbonate. The said sodium carbonate solution in the absorber 4 absorbs hydrogen sulphide from the counter-currently owing cokeoven gas. The so-treated coke-oven gas leaves the absorber at the top thereof and flows to additional apparatus of the byproduct system throughthe pipe 6. Fouled absorbent solution 3 flows from the bottom of the absorber 4 through a valved pipe 8 into a pumping tank |0 to which also is delivered through a valved pipe |2 freshly made up absorbent. The said make-up absorbent is prepared in a mixing tank I4 to which is delivered water and, for example, sodium carbonate through a pipe I6 and is mixed in said tank. The

fresh absorbent is pumped from the mixing tank' I4 through a pipe |8'bypurnp 26 and throughv the said pipe I2 to the hereinbefore mentioned pumping tank l0. pumping tank I is driven by a pump 22V through pipe 24 into the top of an actier column 26 and distributed through nozzles 28" in.- a descending.- flow down over packing in said column. In-the'- actier 26 the fouled absorbent isv lbrought into in admixture therewith are owed from the top;

of the actier 26 through apipe 36 into a condenser 32`wherein a larger portion of the remaining steam is condensed; Thence the hydrogen sulphide flows through pipe 34 to a second condenser 66, of smaller dimension in which substantially the remainder of' the steam is condensed. Substantiallydry hydrogen sulphide isV continuously withdrawn' from the said condenser 36 through pipe 38 by a vacuum pump 46 by` which means the entire actication zone is held under less than atmospheric pressure and by which means also the hydrogen sulphide is pumpedthrough a pipe 42f to any point for utilization thereof. Hydrogen cyanide whichisalso recovered from the gas bythedescribed process` can be separated from the hydrogen sulphide by` any of several known processes whereby.v substantially purehydrogen cyanide. and hydrogen sulphide can be obtainedl Fouled absorbent from thel A coke-plant quenching station 44 is equippedv i with a standard bank of nozzles 46 to which water is delivered from storage tank- 48 through pipe-50' and spray header` 52. The quencher isalsofsup-A plied with a set of" auxiliary sprays 541 to which water is delivered from the storage tank 48-1 through thepipe 50 and a spray header 56. This: auxiliary spray is disposed in a horizontal planeabove the standard spray nozzles 46 and isi soi arranged that the Water spray therefrom willi fall through steam that rises from hot coke in quenching car 58 and has been formed by. theevaporation by the said hot coke of waterfrom the sprays 46. This extra spray lowers the rate of waterA loss by reducingl the release of steamto the atmosphere and also provides a quenching liquor at slightly higher temperature which increases the usefulness of'l the quenching liquor in supplying heat to thegas purification process; The quenching liquor from each quench drains through a pipe 6U into a storage sump 62 called' a hot well. A baffle or screen 63 may beplacedy in this hot welll to screen out breeze and coke abrasive matter from the quenching liquor. Hot

quenching liquor' is withdrawn from this hot wellL through a pipe 64 andv is pumped by a pump 66l through a pipe 68 into the coils of a reboiler 1U? inthe base of the actifier 26. The cooled liquor flows from the reboiler 'In througha pipe '|125 into;

a second storage sump 'I4 termed the cold well, to which make-up water can be delivered through a pipe 'I6 and from which the relatively cool quenching water is pumped by a pump 18 through a pipe 19 and into the storage tank 48.

The heat of the quenching liquor in the reboiler 'I6 that is transferred into the absorbent solutionin the actifier boilsL the solution under the reduced pressure of the actifier and produces the said vapors which flow countercurrently to the downfiowing foul solution and actify it as aforementioned.

Actied absorbent is withdrawn from the bottom of the said actier 26 through the pipe 80 and is pumped by pump 82 through a pipe 84 to a cooler 86 that is conveniently supplied with inlet andA outlet cooling-water pipes 68 and 90, respectively. Cooled, actied absorbent is flowed from the said cooler 86through valved pipe 92 to the top of the said absorber 4 into which it is sprayed by nozzles 94'upon the packing provided therein;

Condensedsteam is flowed from the said condensers 32 and 36 through pipes 96 and 98 respectively into a'pumping tank |00. Collected, condensate is withdrawn by a pump |62 from thesaid tank |00 through a pipe |04 and is pumped into the bottom-of the absorber 4 at which point the condensate is mixed with fouled absorbent in order that it may simultaneously be actied andv treated for removal of any hydrogen sulphide dissolved therein.

In a secondembodiment of the present invention as illustrated in Fig. 2, substantially an identical gas purification system proper is em-` ployed and the same characters of reference are,` therefore used, wherever practicable, topoint .out identical parts and simplify the description.

|Ihus, coke-oven gas is purified in an absorber 4; the fouled solution is delivered therefrom to` thev actifier 26'. and is actied therein under sub atmospheric pressure. The actied solution is; withdrawn from the actifier 26 and is pumped; through a cooler 86 and intothe top of the absorber 4 for thepurication of further quantities ofv coke-oven gas.

Here again a coke plant quenching station 44:, is equipped. with two sets of sprays 46 and 54 and. for the same purpose. Quenching liquor there-4 from drains toa hot well 62 through a pipe 66 and is pumped byA a pump 66. from the well4 62: through a pipe 68 into a vaporizer |05. Thev atmosphere within the shell of.l thevaporizer |05-, is maintained at the reduced pressure of vacuum; actier 26 and. consequently when the relatively" hot quenching liquor is discharged into the va4 porizer` a portion of the liquor vaporizcs while theremainder.` thereof which has been cooled by," the` vaporization flows to the bottom thereof. The said vapors flow into the actifier 26 throughi a pipe |06 and ascend therein in countercurrenta flow in respect of descending fouled solution. The said vapors sweep the hydrogen sulphideand' like gas from theV fouled solution by eect` ing a removal of the partial pressure of hydrogen.` sulphide in the vapors in the actier and thus: byv such direct contact actify the absorbent s0lu.. tion. The introduction of a smallV amount off supplemental heat may be found to increase-the eiiiciency of the process and' often would be'` needed' especially if the described additional" quenchingsprays were not installed. Accordeingfly a small steam` coil |68 is shown in theibase of: the actifier 26;

' 'I-heso--formed vapors and' gases containing hydrogen sulphide pass from the top of the actiiier through a pipe |I0 and into a relatively large condenser I I2 in which a major portion of the vaporized quenching liquor is condensed. The condensate flows through a pipe I I4 into the top of a stripping column II6 in which the condensate is stripped of its hydrogen sulphide by the stripping action of vapors formed by boiling the condensate in the base of the column ||6. rlhe column acts as a reflux condenser and returns substantially all the evaporated liquor to the base of the column. Hydrogen sulphide and like gases liberated in this column ow through pipe I I8 and are returned to the gas flow in pipe I I0. Heat for the stripping column is supplied by a small steam coil |20.

Condensate iioWs from the bottom of the co1- umn I|6 through a pipe |22, and together with the condensate from vaporizer |05, which flows therefrom through a pipe |24, is pumped by a pump |26 into a cold well 14. Make-up water can be delivered through a pipe 'I6 into the cold Well and quenching water is pumped therefrom by a pump 18 through a pipe 19 into the storage tank 48.

Gases containing hydrogen sulphide in preponderance and from which the major portion of water has been removed ow from the condenser II2 through a pipe |28 to condensing and vacuum-pumpin-g means as hereinbefore described and illustrated also in Fig. 1.

`It has been found that, particularly when employing the described auxiliary sprays, there is suiiicient heat from the quenching liquor produced in quenching the total output of coke from a coke-oven battery to provide for substantially complete removal of hydrogen `sulphide and hydrogen cyanide from the total gas output of such battery. The auxiliary heat supplied in coils |08 and |20 in Fig. 2 is comparatively small and can be conveniently supplied with low pressure steam or can be readily supplied with a portion of the hot quenching liquor as when its volume is increased by the extra water that is used in the auxiliary sprays.

, vIn an example of operation according to the method of invention illustrated in Fig. 1, water at 140 F. sprayed from the upper nozzles 54 was raised in temperature to'17'7 F. by condensing steam in the quenching station 44. By

these sprays 8% of the heat which is ordinarily lost with the steam is recovered. A larger quantity of water at 140 F. is sprayed on the coke from the standard sprays. The average temperature of the water in hot well 62 is 185 F. In another instance where intermittent quenching was employed, that is, when the coke is quenched for a short period of about one-half a minute, and then, after a moment, it is quenched again for approximately an equal period, the temperature of the quenching liquor from the rst period was 188 F. and from the second 182 F. The hot vacuum actier is operated at a temperature of 135 Al1". The quenching liquor at 185 F. is delivered to the reboiler, 'I0 wherein its heat is employed to produce vapors in the actiiier for removal of hydrogen sulphide. Based on the average range of hydrogen sulphide concentration in the gas and the usual practicably attainable vacuums a temperature of at least about 125 F. is required to provide substantially complete actification. The water leaving the reboiler has a temperature of about 149 F. On the basis of the heat obtainable from quenching the coke from one oven and purifying the gas from one oven, the `heat load of the vacuum actifler is 177,000 B. t. u. The regular quenching procedure, on the basis of the above temperatures `and a quantity of quenching Water of 3600 pounds, furnishes 72% of the required heat. The remainder is obtained by the said recovery of 8% of the heat formerly lost in the steam. The data of the above example is based on relatively complete purification of the gas.

The above-described process in addition to purifying coke-oven gas in respect of its hydrogen sulphide content provides as a product of the method a technical grade hydrogen sulphide that is suitable for the manufacture, for example, of sulphuric acid.

The herein described invention can be employed to improve the eiciency of any process for liquid purification wherein the fouled liquid absorbent containing a constituent which has been scrubbed from a gas or extracted from a liquid is actiiiable under subatmospheric pressure by heating the same. An example of a liquid purification process similar to the one herewith described comprises the use of Water to absorb ammonia and hydrogen cyanide from raw coke-oven gas, the water containing the absorbed gases being thereafter actiable by heating at subatmospheric pressure. Aqueous absorbents can be, for example, water, aqueous solutions of potassium, sodium or other alkali metal carbonates and bicarbonates, solutions of alkali-metal salts of other weak acids, or solutions of weak bases such as organic amines. I'he absorbable constituent in coke-oven gas (coal gas) can be hydrogen sulphide, hydrogen cyanide, carbon dioxide, ammonia, light oil or carbon disulphide. The light oil and carbon disulphide can be recovered by scrubbing coke-oven gas with `a straw oi1 and the light oil be stripped therefrom, under vacuum, by heat from the said quenching liquor. Such light oil for example can be purified in respect of removal of its hydrogen sulphide content by extraction of it with an alkaline aqueous solution which can thereafter be reactied under vacuum by the low-temperature heat recoverable from the quenching liquor.

As can readily be seen from the foregoing description the process of invention as hereinafter claimed, includes Within its scope continuous operation of the improved liquid purification process and continuous recycling of absorbent solution and also quenching liquor.

The process as particularly described and as claimed is primarily adaptable to continuous operation. Although the invention as hereinbefore set forth is embodied in particular form and manner it may be variously embodied within the scope of the claims hereinafter made.

We claim:

1. A process for the separation of an absorbable constituent from coke oven gas, comprising: scrubbing the coke-oven gas with a liquid absorbent and absorbing coke-oven gas constituent therefrom; removing fouled absorbent containing the absorbed constituent from the absorption zone and flowing the same through an actication zone under less than atmospheric pressure; utilizing the heat at relatively low thermal head of hot quenching liquor from a coke quenching system to generate water vapor in the said actification zone and therewith sweep constituent, as a gas, from the fouled absorbent; preparing the said liquor by spraying the hot coke with water in two quenching stages, of which the second stage comprises spraying Water into the steam evolved by ,fugace 7 the quenching step of the first stage and condensing a portion of the steam; and removing the so-liberated gas from the actiiication zone.

2. The process for the separation of an absorbable constituent of coke-oven gas, comprising: scrubbing the coke-oven gas with a liquid absorbent and absorbing coke-oven gas constituent therefrom; removing fouled absorbent containing the absorbed constituent from the absorption zone and owing the saine through an actication zone under less than atmospheric pressure; utilizing the heat at relatively low thermal head -of ho't quenching liquid from a coke-quenching system to generate water vapor in the said actication zone and therewith sweep constituent, as a gas, from the fouled absorbent, the hot quenching liquor being maintained at a temperature of at least about 170 F. by spraying hot coke with quenching water recirculated from the actif-loation zone at a temperature of about 140 F., and in two stages, of which the second stage comprises spraying water into the steam evolved by the quenching step of the rst stage and condensing a portion of the steam thereby providinga further volume of quenching water of the required temperature; and removing said liberated gas from the actication zone.

3. In the byproduct coking of coal to produce coke, coke-oven gas, and byproducts thereof, a process for the liquid purification of coke-oven gas and recovery of hydrogen sulphide therefrom comprising: scrubbing the total output of cokeoven gas from a coke-oven battery with an alkaline aqueous absorbent and absorbing hydrogen sulphide therefrom; removing fouled absorbent containing the dissolved hydrogen sulphide from the absorption zone and flowing the same through an actication zone under less than atmospheric pressure; quenching all of the coke of only the said coke-oven battery With Water of sufcient volume therefor; condensing a portion of the steam evolved by the quenched coke with a further quantity of water; flowing it and the condensate onto the coke being vquenched thus to aid in quenching and also to mix with the quenching liquor; liberating hydrogen sulphide from the said absorbent in the actication zone by means of heat transferred thereto from the hot mixed quenching liquor; recirculating the so-actied solution to the contact of further quantitles of'coke-oven gas; and removing liberated hydrogen sulphide from the actiflcation zone.

4. In the byproduct coking of coal to produce coke, coke-oven gas, and byproducts thereof, a process for the liquid purification of coke-oven gas and recovery of hydrogen sulfide therefrom comprising: scrubbing coke-oven gas from a cokeoven battery with an alkaline aqueous absorbent, and absorbing hydrogen sulfide therefrom; removing fouled absorbent containing the dissolved hydrogen sulde from the absorption zone and owing the same through an actiflcation zone under less than atmospheric pressure; quenching all of the coke of the said coke-oven battery with water of sufcient volume therefor and in two stages of which the second stage comprises spray ing water into the steam evolved by the aforesaid quenching step to condense a portion of the steam and provide a further volume of quenching liquor of required temperature, flowing quenching water employed in the second stage and condensate formed thereby upon the coke being quenched thus to aid in quenching and also to mix with quenching liquor from the first stage; liberating hydrogen sulfide from the said absorbent in the actication zone by means of heat transferred thereto from hot mixed quenching liquor; recirculating so-actied solution into Contact with further quantities of coke oven gas; and removing liberated hydrogen sulfide from the actiflca.- tion zone.

5. The process as claimed in claim 4 wherein the hot quenching liquor is maintained at a temperature of at least about 170 F. by spraying hot coke with quenching water recirculated from the actification zone at a temperature of about 140 F.

JOHN MITCHELL. HERBERT A. GOLLMAR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Gollmar June 26, 1945 Certicate of Correction Patent No. 2,464,824. March 22, 1949.

JOHN MITCHELL ET AL. It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 1, line 33, before the Word interchange insertl heat;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case inthe Patent Oce.

Signed and sealed this 6th day of September, A. D. 1949.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

